Prehistoric Life 6

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Silurian Period (438-408 million years ago)

The Silurian Period was named for the Silures (1835), another ancient Welsh tribe. Its fossils were recognized as distinct from those of the preceding Ordovician and following Devonian periods. Its beginning formally is defined by the first appearance of the graptolite species Akidograptus ascensus.

Life on Earth. During the Silurian, the Earth generally showed a warming trend after the ice age that ended the Ordovician. The Silurian reefs, which continued to be based mainly on stromatoporoids and tabulates, were huge. Brachiopods and bryozoans (including a number of colonial, massive stony or sea-fan-like forms) dominated the species count, but corals and echinoderms increased in importance. Nautiloid cephalopods and graptolites largely disappeared by the beginning of the Silurian. Eurypterids (sea scorpions, a group of chelicerate arthropods) appeared in the Silurian, some reaching 10 feet long. Jawless, armored fishes (Agnatha) became more diverse.

A significant step was the appearance of the first vertebrate jaw by the late Silurian, developed from gill arches in the first placoderm fishes and early sharks.  Diversifying early land plants were joined by the first fungi. The first terrestrial chelicerate arthropods (scorpions and eurypterids) had appeared by the end of the Silurian. These were very similar to marine forms of both groups. For instance, Brontoscorpio was an earlier Silurian marine scorpion, very similar to the familiar scorpion shape, which reached 3 feet in length. Genetic studies tie insect origins to crustaceans like today’s fairy shrimp and water fleas, the split occurring near the end of the Silurian. Also, millipedes and centipedes (which evolved in the Devonian) appear to be connected to chelicerate arthropods.

One place where the Niagaran formation is at the surface is at the tip of the Bruce Peninsula in southern Lake Huron.

Local landscape. Our area was a shallow, clear, saltwater sea with abundant dome-shaped reefs. The reefs were part of a barrier reef system surrounding the Michigan Basin. The rock is composed of dolomite, which is a limestone (calcium carbonate) in which magnesium replaces part of the calcium, the replacement possibly having occurred after the limestone was deposited. DuPage County’s bedrock thus is a part of the Silurian layer called the Niagaran formation, which forms a bedrock ring including the western shore of Lake Michigan, the Door peninsula, the southern shore of the U.P., the islands dividing Lake Huron from Georgian Bay, and a zone connecting to Niagara Falls, with large areas curving through Indiana and parts of Ohio. Outliers can be found in eastern Iowa. Our area probably was between the equator and 20° south latitude. The big Thornton Quarry on either side of Interstate 80-294 is mining one of the larger known reefs in this formation.

This structure, referred to as a “flowerpot,” is an isolated pillar of the Niagaran dolomite. It is on an island just off the tip of the Bruce Peninsula.

Local life. Fossils of the Niagaran formation found locally include reef-forming corals (including antler forms and large lumps such as Cladopora reticulata, Halysites catenularia and Favosites niagarensis). Other attached forms include rugose (horn) corals (Asthenophyllum racinensis, Dalmanophyllum wisconsinensis, Pycnostylus guelphensis); bryozoans (Fenestrellina spp., Hallopora ellengantula, Pachydicta crassa); calcareous algae (e.g., the plum-shaped green lump Calathium egerodae); and stromatoporids. Chert nodules are thought to have been derived from the hard parts of sponges (great for arrowheads, lousy for stone crushing machines), but at least one identifiable fossil sponge is known, Calathium sp. The diverse brachiopods include Eospirifer(Spirifer) radiatus, Apopentamerus racinensis, Leptotaena (Leptaena)  rhomboidelis, Rhynchotreta cuneata, Atrypa reticularis niagarensis, Schucheretella subplana, Uncinulus stricklandi, Meristina maria, Conchidium laqueatum, Kikidium, and Wilsonella. There also are several species of crinoids (Crotalocrinites cora, Lampterocrinus infatus, Marsupiocrinus chicagoensis, Siphanocrinus nobilus, Eucalyptocrinus crassus, Periechocrinus infelix), and crinoid-like cystoid echinoderms (Caryocrinites ornatus, Holocystites alternatus)

This diorama is part of the Evolving Planet exhibit at the Field Museum of Natural History. It portrays a Silurian reef.

Mobile life forms include trilobites (Bumastus niagarensis, B. harrisi, B. insignis, Calymene celebra, C. niagarensis, Arctinurus chicagoensis, Dalmanites sp., [=?] Dalmanella platycordata), and mollusks (snails Euomphalopterus halei, Tremanotus alphaeus, T. chicagoensis, Straparollus magnus, Lophospira rotunda, Phanerotrema occidens; pelecypods Mytilarca denticostia, Matheria recta; straight-shelled cephalopods Amphicyrtoceras orcas, Dawsonoceras bridgeportensis, Kionoceras orus, K. cancellatum; and at least one coil-shelled species, Discoceras marshi).

This fossil trilobite is in one of the Silurian dolomite flagstones at Fullersburg Woods, mined from the Lemont Quarry and used by the Civilian Conservation Corps in its construction projects at that forest preserve.

The earlier Alexandrian series, also dolomite, has the brachiopods Platymerella manniensis, Microcardinalia pyriformis, and Pentamerus oblongus.

Vertebrates, i.e., fishes, continued to be relatively uncommon through at least most of the Silurian, and apparently fossils of them have not been found locally.

The Shape of Salt Creek

by Carl Strang

Back when my office was at Fullersburg Woods, I had two occasions to study old maps and aerial photos of that forest preserve. Both when looking at the history of periodical cicadas in DuPage County, and when examining Fullersburg’s archeology, I found myself comparing original survey maps from the first half of the 19th Century to the 1874 county atlas to the earliest aerial photos from 1939. Though not central to these investigations, I couldn’t help but notice inconsistencies among these maps and photos in the shape of Salt Creek. Let’s begin with the 1939 aerial photo and work back.

Salt Creek enters Fullersburg in the upper left (NW) portion of the photo when it passes beneath 31st Street. The stream proceeds south, with the interruption of a small hairpin turn, before turning east. After a significant straightaway the stream turns back north, takes a big swing east and divides to surround Willow Island as it begins a long stretch flowing south, then turns SE until it exits the preserve soon after passing beneath York Road. Salt Creek today has essentially the same configuration. Let’s look next at the 1874 atlas.

For the most part Salt Creek looks similar to its present day configuration. There is one significant exception, however. In the next image I superimpose the 1874 map onto the 1939 photo.

The red line I have added to reconcile the two versions. It makes sense. That line traces the bottom edge of a sharp bluff, the edge of the Tinley Moraine. The following photo shows where one end of the adjacent lowland, cut off as the red line shows, meets the morainal bluff.

It appears that the streambed migrated between 1874 and 1939 to create that low peninsula. The concrete slab in the photo, part of an abandoned trail installed during the Great Depression by the Civilian Conservation Corps, bridges what is left of the 1874 channel. Now let’s shift to pre-1850, when the original land survey gives us the first record of Salt Creek’s shape.

This surveyor’s sketch map is based on an original 1822 record. This is significantly different from the later map and photo. Again I superimpose.

The red line again reconciles the two, and again it makes sense. The area along the red line is low, and in fact at times of flood, water sheet-flows through there, short-cutting across the base of the river bend (though most continues to follow the main channel).

What brought this back to mind was an observation I made recently, something I hadn’t noticed before, when looking at the original survey notes associated with the earliest map. The surveyor noted that the width of Salt Creek up and down the stretch now part of Fullersburg was 20-30 links. A link in the surveyor’s standard measuring chain was only 8 inches long, so that Salt Creek prior to American settlement was only around 15 feet wide. Today it’s much wider.

The 1800 width of the stream was closer to that of the central channel through the ice in this photo than to today’s banks. The picture I am left with is of a relatively small stream, wandering over the low area between the Tinley and Valparaiso Moraines. As DuPage County became agricultural, then urban, increased runoff ballooned Salt Creek’s width and volume. The growing stream carved a channel that has become more stable. The change between 1874 and today suggests that Salt Creek at least began to cut its way back to the early-1850’s channel route. However, downward erosion may have set the main channel in a shape that will resist future alteration.

Fullersburg Archeology: A Mystery

by Carl Strang


It’s time to conclude my series on Fullersburg Forest Preserve history and archeology. Time to put on the pith helmet one last time and check out a mystery. And if you can cast light on it, I will appreciate the assist.


If you take the informal dirt trail clockwise around the edge of Butler Woods from Rainbow Bridge, it will take you to the Hairpin Turn.




Shortly after you go around that turn you will see a branch of the trail heading right (east) and up the hill. At the top of the hill is a trench, dug no doubt for some agricultural purpose. It’s not a glacial feature.


Just below that trench is a trio of concrete structures whose function at present remains a mystery. These include a 25-foot-long, arc-shaped low wall built of 2’x2’ concrete blocks, one of which is being shifted as a large white oak grows in behind it.




This arc’s concave side faces south, and in the focus of that arc 30 feet further south there is a bunker-like structure 8’ wide, 7’ deep, and 3’ tall, open on the south side with some dolomite flagstones stacked in the bottom, an old decaying piece of lumber on the ground, a few red bricks scattered on top, and an iron ring set in the center of the roof piece on its south edge.




This bunker is dug into the side of the hill. Brookfield Zoo educator Jim Ritt has made the interesting suggestion that the structure was designed for dynamite storage. Its orientation away from farm clearings and buildings to the north that show on the 1939 aerial photo is consistent with this hypothesis. Back, now, to the trail. On the north side of that trail, roughly in line with the center of the arc and the bunker and 10 feet north of the wall, the third structure is a 3’ circular piece of concrete with a rectangular slot through its top that is about the length and depth of one of the wall’s elements.




The axis of that slot is in line with the bunker. These objects are within a string of older trees that are visible in the 1939 photo. Incidentally, piled in a refuse heap a short distance north of there, just south of the swamp and east of the Hairpin Turn, is a rusting tank of the sort used for heating oil in a home furnace, along with two rusted crushed objects which may be identical tanks, and a wheel still bearing its tire.




So that’s where I’ll end this topic, at least for Fullersburg. There are some other archeological features on that preserve I haven’t mentioned, but I’ll leave them, along with the ones I never found, for your own discovery.

Fullersburg Archeology: Old Building Foundations

by Carl Strang


Two old building foundations are waiting your discovery in northern Butler Woods. The informal dirt peripheral trail crosses one of these,




very close to a roadside sign and boulder which indicate that this was where a hunt club paused before crossing 31st Street in the old days. I wonder if this building might have been a rest shelter for hunt participants. If not, it probably was a farm outbuilding.


The second foundation clearly was a home.




It is located near the 31st Street Stem trail, west of Butler Prairie. The stone boundary of a foundation flowerbed still can be seen. An old trail or drive extends south from the west edge of the house. That this area was agricultural is supported by the presence of drainage tiles in the Butler Prairie area. The north edge of the forested block southwest of this house still can be seen as a straight boundary between older trees, and younger ones that have grown up post-agriculture. Many years will pass before the influence of this stage of Fullersburg’s history disappears from the forest.

Fullersburg Archeology: Butler Woods Trails

by Carl Strang


In a series of earlier posts  I reviewed surviving ruins as well as structures still in use that were constructed by the Civilian Conservation Corps at Fullersburg Woods Forest Preserve. Now is a great time to explore the ruins of Fullersburg, with temperatures warmer and obstructing vegetation not yet in leaf. Today I want to look at some fading signs of events at this preserve that followed the Great Depression, focusing on Butler Woods. Here is a map with place names.




The improvements made by the CCC, plus the limited number of other preserves available at the time, drew crowds to Fullersburg Woods. It was too much of a good thing, and by the 1960’s Fullersburg was regarded as suffering from overuse. The boat house was closed, and that building was converted to the Visitor Center, which opened on May 2, 1973. The addition of other forest preserves eased the pressure, allowing Fullersburg to recover. In 1975, Butler Woods was added via a 30-acre donation by the Butler Company, plus a 40-acre purchase. The 31st Street Stem trail was constructed to connect York Road to 31st Street through the preserve. New trails were developed through the Butler Woods addition. Except for the main trail along Salt Creek and the 31st Street Stem, these have always been dirt paths and are no longer maintained. Most of them continue to be used enough by people and deer that they still can be followed easily. Some railroad-tie steps remain in place where the trail climbs the hill at the end of the Hairpin Turn, and a few unused ties still are piled below there. Slight alterations in the trail route have accumulated over the years, possibly originating when tree falls forced detours. In addition, a new route developed after the 1970s which skirts the northern edge of the preserve along 31st Street. The old trails east of the 31st Street Stem now are almost exclusively the province of deer.


One approach to finding the disused trails east of the 31st Street Stem is to make your way along the south boundary of Butler Prairie. Along the way you may see the drains at each end of the prairie, both eroded over time so they seldom will be reached by flood waters.




Above the westernmost of these drains are concrete pieces that appear to be a corner and other bits of wall.




At the east end of the prairie, in addition to scattered pieces of brick from an earlier age, is one of the old trails, which still (in 2008) is fairly easy to follow southeast from there. Eventually that trail peters out into a deer trail that bends more straight east. With some effort you may be able to find one or both of the old human trails that descended to Salt Creek. These joined the trail you are on just after it curves east, with one essentially going straight south downhill, and the other angling more southwest. Both are marked by clear worn depressions, though fortunately neither has gullied. The more distinct one goes straight down hill. If you look carefully you can see the remains of timbers installed as steps or check dams. The most intact of these timbers is at the bottom of the old trail, which joins the main trail about 20 feet east of a bench.




If you choose to find this trail from this bottom end, note that there is a recent unofficial path angling down from the church parking lot. This joins the main trail at the same point. The historical trail heads straighter north, straighter uphill, and is less obvious. Look for that timber step. The place where the other branch of the historical trail joins the main trail at Salt Creek is obscure. To find it, follow the east bank of the little stream that passes under the main trail a short distance west of the same bench. This is the stream that originated at the westernmost of those two stranded storm drains. 10-20 yards from the main trail, look for the shallow depression marking where the historical trail angles NE up the hill.

Fullersburg Archeology: Closing the CCC Chapter

by Carl Strang


Visitors to Fullersburg Woods Forest Preserve experience works created by the depression-era Civilian Conservation Corps whether they know it or not. Most of the trails, the parking lot, bridges, dam, visitor center and trail structures were created by workers in the Fullersburg CCC camp. I have shared some of the ruins of other works that no longer are in use, and want to close the CCC chapter with a few more.


The 1937 map that has been our guide to CCC projects shows a number of latrines and “incinerators.” Some of the latrines still are in use, though updated and maintained by the Forest Preserve District. I provided directions to ruins of a latrine and possible incinerator yesterday . Now I want to cover the rest.


We’ll start at Willow Island, which itself probably was created by the CCC , reached by taking the trail north from the Visitor Center and crossing the little bridge.




On Willow Island, the still standing structure at its southeast corner is a picnic shelter, the one on the east side held a well. The spot marked “Incinerator” in the center of the island is our first ruin, a hollow cube of concrete set flush with the ground and bearing 3 holes broken in its top.




A short distance north of that cube is a rusting wire cylinder that once may have been the actual trash burning container.




Please remember not to disturb any artifacts you may find. The figure-8-shaped large channel in the southeast part of Willow Island was dug after the CCC was done, in a since abandoned attempt to provide an area for wildlife viewing.


Crossing back over the Willow Island Bridge and turning west to follow the trail around the Interpretive Trail river bend, you will pass a pump not marked on the map, a tiny shelter, and the functioning latrines shown on the 1937 map. I could not find a trace of the adjacent incinerator. The original support beams of the shelter at the northeast corner of the river bend were rotting, and replaced by octagonal planed beams in 2007. Our next ruin is one of the latrine vaults near the north end of the bend.




I could find only one in the area marked, but tall dense growth of garlic mustard and dame’s rocket obscured much of the ground that day.


We finish in the area of today’s buildings around the north end of the parking lot. Well #2 is not there, as far as I can see. There is an old broken concrete slab where an Incinerator is marked on the 1937 map, across the service road from the west end of the garage. 




That concludes our archeological adventure for now. The next chapter will take us into parts of the preserve that were added after the CCC era. But in our current time of economic uncertainty there is something to be said for exploring works that date back to a period that historians still call the Great Depression.

Fullersburg Archeology: A Former Picnic Area

by Carl Strang


Today I want to plant another idea for those who might wish to search out archeological ruins from Fullersburg Forest Preserve’s past. This might be a good expedition for late winter or early spring, after the snow has melted and before the woody plants leaf out. The ground might be wet or muddy in that season, so footwear should be selected carefully. This can be done on a warm sunny summer day, too, but leafed out shrubs will make the search more challenging.




In Fullersburg’s early heyday after the improvements made by the Civilian Conservation Corps , there was a picnic ground in the triangular area on the east side of Salt Creek, just downstream from the Visitor Center Bridge and across from Sycamore Island. The most conspicuous surviving structure is a grill or incinerator.




It is located close to where an unlabeled circle is marked on the map, northwest of where the labeled incinerator was crossed off (is this the relocated “incinerator?”). One of the latrine vaults still can be readily found.




If there was a second one, it is more obscure. Someone thoughtfully placed a log in it to ease the escape of any animal that might fall into the hole. Existing, but a little more challenging to find, are the ruins of the Shelter and Well #1. The shelter was at the northwest corner of a relatively elevated area, and must have provided a beautiful view of Salt Creek. Today all that remains are scattered bits of stone and concrete at the surface of the soil.




South of there, Well #1 no longer bears its shelter, but remains as a square of concrete with the circular center pump mount still in place.




Tomorrow I will conclude the CCC chapter of Fullersburg’s history.

Fullersburg Archeology: Structures Still in Use

by Carl Strang


Today I want to continue reviewing the Civilian Conservation Corps chapter in the history of Fullersburg Woods Forest Preserve, this time focusing on some structures that still stand.


I’ll begin with the single remaining “Trail Shelter” marked on the 1937 map. Earlier I described some of these shelters that today are represented by only a few foundation stones. The standing one is very simple, and you can find it by traveling north from the Visitor Center, turning left just before the Willow Island bridge, and looking on your right.




This is simply a bench with a roof.


I long was puzzled by the different forms of shelters, sometimes so close together as to question what the builders had in mind. The map made this clear, however. Some of these structures have substantial beams and are larger.




They come in various shapes, but have in common the large round beams, which were formed from the trees that were cut to create the main parking lot, and the dolomite stone slabs, which came from the Lemont Quarries. All are simply marked “Shelter” on the map, and apparently were intended for picnics and other group activities.


The other common trail structure design has a square shape and smaller beams with square cross sections.




These are marked “Well” on the map, and originally contained pumps. Their frequent proximity to the shelters is explained as the provision of a water source for picnickers. None of these house pumps today.


The most substantial building left by the CCC is the Visitor Center, which they intended as a “Boat House”




In Fullersburg’s heyday as the most popular property in the then much smaller Forest Preserve District of DuPage County, this building was known as The Landing and indeed housed a boat concession from which people had excursions on Salt Creek.




It likewise is characterized by the use of large round beams and dolomite slabs in its construction. The CCC did a lot more at Fullersburg. Stay tuned.

Fullersburg’s Abandoned CCC Trail

by Carl Strang


Yesterday I introduced the Civilian Conservation Corps chapter in the history of Fullersburg Woods Forest Preserve. Today I want to describe an abandoned CCC trail that awaits exploration by the adventurous.




The area is on the north side of Salt Creek in the western part of the preserve. Except for a narrow strip of land along the stream bank, and the low triangular area downstream from the Rainbow Bridge (the bridge at the western extremity of the preserve), the north side of Salt Creek still was in private hands in the days of the CCC. They apparently dealt with the challenges posed by this low area of flood plain by piling fill, installing concrete culverts, and cutting into the side of the hill (reinforcing above and below with walls of dolomite slabs) to build a two-branched trail.




That trail now is so overgrown that navigating it provides something of a challenge, but is easier in winter with vegetation down. The trail does not exactly follow the route indicated on the 1937 map. Walking east from Rainbow Bridge, and looking to the right shortly before today’s trail begins to climb the steep hill (the Tinley Moraine), you can see the old elevated trail route punctuated by a concrete culvert.




That elevated fill is well populated with honeysuckle now, but if you follow it you will find it curves left and soon reaches the edge of Salt Creek. The trail there goes along the edge of the creek in both directions, completely outlining the creek edge of that low piece of ground. Following it east (left) you will cross another concrete culvert,




and eventually reach where the abandoned trail climbs up to rejoin today’s trail. As you do, keeping an eye out for poison ivy and stumbling over the trunks of fallen trees, you will note the stacked dolomite wall that reinforced the stream bank to your right,




and the similar retaining wall built into the hillside to your left.




If you accept this challenge, you will be training your eye to detect old human changes to the landscape. That experience will improve your ability to detect such influences in other places you may choose to explore.

Fullersburg Archeology: Trail Shelters

by Carl Strang


Fullersburg Woods Forest Preserve was the site of Civilian Conservation Corps camp #V-1668 in the 1930’s. In 1933, in response to the economic calamity of the Great Depression, Franklin Delano Roosevelt started the CCC in the first two months of his presidency. By the end of that year, two camps had been established on forest preserves in DuPage County, at McDowell and Fullersburg. Young (late teens to early twenties) single men moved into the camps, enrolled for 6 months at a time and could extend to 2 years. The camps were run by the army, but the work was directed by foresters and other specialists. At Fullersburg the camp was located at the present Hilltop Prairie. In 1937, the year before the Fullersburg camp closed, a map was prepared that shows a number of structures that had been built or were under construction.




The CCC built the Visitor Center and other buildings I will highlight in some future posting. Today I want to focus on a series of structures, labeled “Trail Shelters” on the 1937 map and represented there by little black rectangles, that no longer stand.




They are not entirely gone, however. Guided by the map, I went to these locations to see if any traces of the shelters remained. In a couple cases I found lines of dolomite blocks in Salt Creek along its edge, right where the shelters are marked on the map. Apparently the dolomite pieces, a common construction material used by the CCC, were the floors of the small shelters and have collapsed into the creek.




In one case more remains. This one, across from the northeast corner of Willow Island, still is well represented by its relatively intact dolomite stream bank foundation, and a concrete post support at one end. You have to pick your way through the woods off trail to find it.




These rocks, quarried at Lemont, transported to Fullersburg, forming part of structures for a time and now scattered, remain to speak to us of the preserve’s history. They also add structure and chemistry to the microenvironments where they now sit, serving as shelter or obstacles to small animals. From the standpoint of the stones their present locations still are fresh and new compared to the hundreds of millions of years of their existence.

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